Field of the Invention and Related Art Statement
The present invention relates to a method of detecting a configuration of a tire, and more particularly a method of detecting depressions and protrusions on a side wall surface of a tire.
In radial tires, a steel cord having a number of thin steel wires aligned therein is employed. However, it would be not always guaranteed that the steel wires are aligned at a regular pitch. That is to say, spaces between adjacent steel wires might become wider or narrower than a predetermined space. If the space is wider than the standard value, a corresponding portion of a tire side wall surface would protrude when the tire is inflated. On the contrary, if the spaces are smaller than the standard length, the corresponding portion of tire surface is depressed upon inflating the tire. If the tire has such protrusions and depressions, a desired property of tire might be deteriorated. Therefore, it is necessary to check whether or not a manufactured tire has such protrusions and depressions particularly on its side wall portion, while the tire is normally inflated.
Heretofore, the above mentioned checking operation is generally carried out by an operator. That is to say, the operator passes his hand over the side wall surface of inflated tire to find any depressions and protrusions. However, such a checking operation requires a skill and causes human errors.
In order to mitigate such a drawback, in Japanese Patent Application Laid-open Publication (Kokai) No. 56-122,931, there has been propose a method of automatically detecting the protrusions and depressions on the side wall surface of tire. In this known method, use is made of a displacement sensor of an electrostatic capacitance type to measure a distance between the sensor and the side wall surface in a non-contact manner, while the tire is rotated at a constant speed. Then, a displacement signal is processed to detect a configuration of depression and protrusion on the side wall surface, and the detected configuration is compared with a standard configuration to judge the depressions and protrusions.
In the known method of detecting the outer configuration of tire, in order to detect the protrusions and depressions from the analog displacement signal supplied from the displacement sensor, the analog displacement signal is differentiated to detect raising edges and trailing edges of the displacement signal, and these raising and trailing edges are unconditionally determined to be the protrusion and depression, respectively. In such a method, if the displacement signal has a simple waveform, the depressions and protrusions could be detected accurately. However, in general, since the side wall surface has various characters and marks, decorative lines, etc. formed therein, the displacement signal has a rather complicated waveform. Then it is quite difficult to detect the protrusions and depressions on the tire surface in an accurate manner. For instance, in case of detecting a protrusion, only a raising edge of the displacement signal is taken into account, but a next trailing edge is not considered at all, and in case of detecting a depression only a trailing edge is considered, but a next raising edge is not taken into account. Therefore, if a small protrusion is existent in a large depression and if a small depression is included in a large protrusion, these small protrusion and depression could not be detected precisely. In this manner, the known method has a low detecting precision and a reliable detection could not be expected.
Moreover, in the known method since the protrusions and depressions are judged only by width and amplitude of the displacement signal, judged result obtained by rotating the tire in one direction might differ from that obtained by rotating the tire in the opposite direction. Further, since measurement data is processed in an analog manner, the measured data could not be obtained as numeric values. Therefore, only a final judgment is displayed, and it is impossible to analyze intermediate steps for deriving such judgment.